Gripper bar for die cutting machine

ABSTRACT

A hollow gripper bar having a hexagonal profile which reduces the bending and torsional stresses applied thereto by the acceleration and deceleration of the bar in a die cutting machine. The gripper bar includes an upper wall, a spaced lower wall, a leading wall and a trailing wall extending between the upper and lower walls. The leading wall includes a front top portion extending transversely from the upper wall and a front bottom portion disposed at an acute angle with respect to the front top wall portion. The trailing wall is similar in design to the leading wall and includes a rear top portion extending transversely from the upper wall and a rear bottom portion disposed at an acute angle with respect to the rear top portion. Both the front top portion and rear top portion have a thickness that is greater than the thickness of the upper wall. In addition, the front bottom portion as well as the rear bottom portion have a tapered thickness that gradually decreases from the front top portion and rear top portion, respectively, to the lower wall.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to die cutting machines for making box blanks, and more particularly to a gripper bar for use in a die cutting machine.

[0002] Gripper bars are used in die cutting machines to pull sheets of paper material through the machine, and properly position the sheets at various successive processing stations where the sheet may be printed, cut, embossed, creased, and/or stripped of waste. Gripper bars are generally fitted on two lateral chains at regular spaced distances in the machine and extend crosswise to the machine direction, i.e. the traveling direction of the sheets of paper material in the machine. The gripper bars and sheets of paper material follow a circuit composed of successive horizontal intermittent movement from a starting position through the various processing stations. At the downstream end of the machine, the gripper bars move in an upward arc to a return path which then terminates in a downward arc to the starting position where the gripper bar is once again ready to accept a sheet of material and to proceed through the successive processing stations of the machine.

[0003] When the gripper bar is in the starting position, it is properly aligned with a feeder table as well as the various downstream processing stations referred to above. When a sheet of paper material to be processed is pushed from the feeder table, grippers on the gripper bar are closed about the edge of the sheet and the sheet is carried to the first processing station within the machine. Thus, as the sheet is transferred from one station to the next in order to permit cutting, creasing, waste stripping and the like, the gripper bar successively moves between combinations of acceleration, deceleration, dwell, and/or standstill operations.

[0004] As the production speeds of machines increase, a corresponding shorter operating cycle for the gripper bar and sheet of paper material results. For example, it is possible to reach a throughput and production speed of more than 9,000 pieces per hour with a cycle duration at each station of about 0.4 seconds, of which about 0.3 seconds are taken up by movement of the sheet of material and the gripper bar from one station to the next, typically a length of about 1 meter. Since the gripper bars are connected only at their ends to drive chains in the machine, the bending and torsional stresses applied to the gripper bars by acceleration and deceleration are extreme. In addition, the moveable assembly comprising the gripper bar, the grippers themselves, and the accompanying elements for actuating the grippers which are carried on the gripper bar, is relatively heavy which results in a massive high inertia momentum which adds to the bending and torsional stresses applied to the gripper bar. Obviously, over time, the gripper bars become stressed, and should the bar fracture, the resulting damage to the machine and machine downtime is very costly.

[0005] Gripper bars are typically formed to have a hollow cross-sectional profile through which a gripper opening axle extends. The gripper opening axle, which is rotatably mounted in the bar, is driven to open and close the grippers. The gripper opening axle is rotated by means of a lever attached at one end thereof which typically engages a cam mechanism at the above noted starting position to open the grippers. In order to insure that the grippers close tightly about the edge of a sheet of paper material to be processed, a relatively strong spring force is utilized to insure the necessary gripper action against the sheet of material. Consequently, a very strong opening torque is applied to the axle via the lever to open the gripper fingers against the spring force. This strong opening torque provides a stress on the mounting arrangement of the lever on the axle. In the past, this stress has eventually led to a loosening of the lever mounting on the axle resulting in a reduction or the complete elimination of the travel of the tips of the gripper fingers. Obviously, if the gripper fingers do not open, the gripper bar cannot accept a new sheet of paper material at the starting position in the machine. This again results in potential damage and machine downtime.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a gripper bar having a profile which reduces the bending and torsional stresses applied thereto by the acceleration and deceleration of the bar in a die cutting machine.

[0007] It is another object of the invention to provide a gripper bar whose weight will be reduced so as to further reduce the stress caused by the relatively high inertia momentum of prior art devices.

[0008] Yet another object of the invention is to provide a gripper opening arrangement which utilizes a lever that will not loosen to thereby insure proper travel for the tips of the gripper fingers.

[0009] In order to accomplish the above objects, the present invention provides a hollow gripper bar with a unique profile. The gripper bar includes an upper wall, a spaced lower wall, a leading wall and a trailing wall extending between the upper and lower walls. The leading wall includes a front top portion extending transversely from the upper wall and a front bottom portion disposed at an acute angle with respect to the front top wall portion. The trailing wall is similar in design to the leading wall and includes a rear top portion extending transversely from the upper wall and a rear bottom portion disposed at an acute angle with respect to the rear top portion. In a preferred embodiment, both the front top portion and rear top portion have a thickness that is greater than the thickness of the upper wall. The ratio of the thickness of the front and rear top portions to the thickness of the upper wall ranges from about 1.01 to 1 to about 2 to 1, preferably from about 1.1 to 1 to about 1.5 to 1, and most preferably about 1.2 to 1. In addition, the front bottom portion as well as the rear bottom portion have a tapered thickness that gradually decreases from the front top portion and rear top portion, respectively, to the lower wall. The tapered thickness of the front and rear bottom portions range from an angle of about 1° to about 10°, with 5° degrees being preferred.

[0010] In another embodiment, the gripper bar includes an improved mounting for the lever on the gripper opening axle. In this embodiment, the gripper bar includes an elongate bar in the form of a hollow shell defining a longitudinal axis, a plurality of grippers disposed on the bar and spaced at regular intervals along the longitudinal axis and moveable between open and closed positions, a longitudinally extending axle rotatably mounted within the hollow bar for movement between a first position wherein the grippers are closed and a second position where the grippers are open, a plurality of actuators mounted on the axle and spaced at regular intervals to correspond with the grippers so as to be rotatable with said axle to open and close the grippers, a lever disposed at one end of the axle operable to rotate the axle between its first and second positions, and the mounting for the lever on the axle comprises a key formed on the axle, a key-receiving opening formed in the lever, and a clamp for clamping the lever on the axle. Preferably, the key comprises a flat area formed on the outer surface of the axle and the key-receiving opening includes a matching flat section corresponding thereto. The clamp preferably comprises a pair of opposing jaws surrounding the axle, and a retainer such as a bolt for pinching the jaws together to securely mount the lever on the axle.

[0011] Other advantages and features of the invention will be readily apparent from the description of the preferred embodiments, the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings illustrate the best mode presently contemplated of carrying out the invention.

[0013] In the drawings:

[0014]FIG. 1 is a crosswise elevational view of a gripper bar constructed in accordance with the present invention illustrated partially in section and partially in full;

[0015]FIG. 2 is a top plan view of the gripper bar of FIG. 1 also shown partially in section and partially in full;

[0016]FIG. 3 is an enlarged cross-sectional view of the gripper bar taken along the line 3-3 shown in FIGS. 1 and 2;

[0017]FIG. 4 is an enlarged cross-sectional view of the gripper bar taken along the lines 4-4 shown in FIGS. 1 and 2.;

[0018]FIG. 5 is an enlarged exploded view of a gripper opening axle and accompanying lever for rotating the axle; and

[0019]FIG. 6 is an enlarged cross-sectional view showing the mounting arrangement for the lever on the gripper opening axle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Referring now to the drawings, FIGS. 1 and 2 illustrate a gripper bar generally designated by the numeral 1 which is used in a die cutting machine for converting or processing a sheet of paper material into a box blank. These machines are used to cut one or several blanks into each sheet of paper material which, after folding and gluing may be formed into boxes. The gripper bar 1 enables the pulling and positioning of the sheets of paper material within the machine as they are carried through various sequences of printing, cutting, embossing, creasing, waste stripping and/or blanking stations.

[0021] The die cutting machine usually is formed by a series of stations with the first station being a starting position or input station in which the sheets, which may be pre-printed if desired, are taken one by one from the top of a stack to a feed table where they are placed in position against frontal and side guides. The sheet can then be grasped by the gripper bar, which extends longitudinally crosswise of the machine direction. The gripper bar is attached at its opposite ends to a pair of lateral chains which lead the bar, and thus the sheet of paper material in the machine direction or downstream into subsequent processing stations. Typically, the sheet is first conveyed into a cutting station where the box blanks of a desired size are cut into the sheet. These blanks are held to the sheet by nicks which are arranged along the cut edges of the blanks. This cutting station is usually comprised of upper and lower tools one of which is provided with a plurality of line-shaped straight and curved die cutting blades. If desired, the cutting station may be preceded by a printing station, or as noted above, the sheets may be pre-printed. After cutting, the sheet is then lead to a stripping station where the waste, i.e. the unused scrap between the various box blanks, are grasped by upper lower pins in order to be lead downward into a waste container. The sheet is then fed into a blank separating station where the fasten points or nicks between the blanks and the sheet are broken by a tool so that each of the blanks are released and falls onto a stack of blanks below the tool. Finally, the residual or remaining portion of the sheet is carried into a delivery or exit station where it is released by the gripper bar 1.

[0022] A plurality of gripper bars 1 are generally fitted onto two lateral chains (not shown) at regular intervals depending on the length of each sheet of material and extend crosswise to the machine direction or downstream direction of the sheets. As noted above, the chains and attached gripper bars 1 follow an elliptical-like circuit inside the die cutting machine initially composed of successive horizontal translation movements from the starting position or input station along a horizontal path through the various sequential processing stations and then, at the end of the path, i.e. the downstream or exit end, move in an upward arc to a return path which moves the gripper bars 1 back upstream and then terminates in a downward arc to once again be located at the starting position or input station. When the gripper bar 1 is in its starting position or input station, it is aligned with the feeder table and at this stage, the grippers (hereinafter to be described) are opened to receive a sheet of paper material pushed downstream from the feeder table into the input station. Once properly located between the grippers of the gripper bar 1, the grippers close to grasp the front or leading edge of the sheet whereupon the sheet is carried downstream to the first processing station which, as noted above, is typically either a printing station or a cutting station. Although the die cutting machine is not illustrated in detail herein, the machine and its operation is well known to those skilled in the art and therefore it is believed not necessary to illustrate the machine in detail herein.

[0023] As used herein, the terms “upstream” and “downstream” are used in reference to the direction of displacement of the sheet of paper material, which is shown by arrow 2 in FIG. 2. Arrow 2 illustrates the machine direction, i.e. the downstream or material processing direction for the sheet. Thus, upstream typically refers to a direction toward the entrance of the machine whereas downstream refers to a direction leading to the exit of the machine. Likewise, the term “leading” refers to the downstream side of an element wherein the term “trailing” refers to the upstream side of the element. In a similar manner, the expression “crosswise” refers to a direction transverse to the machine direction indicated by arrow 2. The term “sheet of paper material” refers to flat , plate-like work pieces or elements, such as planar sheets of paper, cardboard, paperboard, and the like, typically processed into packaging, particularly boxes.

[0024] Referring again to FIGS. 1 and 2, gripper bar 1 defines a longitudinal axis which extends crosswise with respect to the machine direction 2. As shown, gripper bar 1 has a hollow hexagonal profile defined by an outer shell having an upper wall 3, a lower wall 4, a leading wall 5 and a trailing wall 6 (see FIG. 3). Opposite ends of gripper bar 1 are attached by mounting plates 7 and 8 to drive chains (not shown) of the die cutting machine in a conventional manner.

[0025] A plurality of grippers 9 are disposed on bar 1 and spaced at regular intervals along its longitudinal axis. Grippers 9 are moveable between open and closed positions to grasp the leading edge of a sheet of paper material at the input station to pull the sheet through the machine and to release the sheet at the exit end of the machine. As shown best in FIGS. 3 and 4, each gripper 9 includes an upper finger 10 and a lower finger 11. Upper finger 10 is mounted at its leading end to leading wall 5 by means of a pair of screws 12. Finger 10 also includes an S-shaped portion 13 which leads to a horizontal portion 14 which extends across the outer flat surface of upper wall 3 of gripper bar 1 and extends upstream or rearwardly to a knuckled tip portion 15 which projects rearwardly beyond trailing wall 6. Lower finger 11 is in the form of a right angled member having a vertical leg portion secured by screw 16 to trailing wall 6. Finger 11 includes a horizontal leg portion 17 extending rearwardly from wall 6 and leading to a serrated tip portion 18. The serrated tip portion 18 interacts with the knuckled tip portion 15 to securely grasp a sheet of paper material therebetween due to the spring force provided by S-shaped portion 13 of upper finger 10.

[0026] As shown best in FIG. 3, tip portions 15 and 18 open sufficiently to provide a tip travel or gap 19 having sufficient height to receive the leading edge of a sheet of paper material therebetween. In order to provide for the opening and closing movement of fingers 10 and 11, gripper bar 1 includes a longitudinally extending axle 20 rotatably mounted within the hollow profile of gripper bar 1 for movement between a first position wherein fingers 10 and 11 are closed and a second position wherein fingers 10 and 11 are open. Axle 20 is rotatably mounted at its opposite ends via bearings 21 and 22 formed in mounting plates 7 and 8 respectively. As shown best in FIG. 3, axle 20 is tubular in shape and extends longitudinally along the longitudinal axis of gripper bar 1 and is typically composed of an aluminum material. In order to rotate axle 20 between its first and second positions for closing and opening fingers 10 and 11, there are provided two levers 23 and 24 securely mounted thereto at opposite ends thereof. Levers 23 and 24 each include a roller 25 and 26, respectively, which engages a cam or other element (not shown) in the machine to raise or lower levers 23 and 24, which in turn rotates axle 20, depending upon whether fingers 10 and 11 need to be open at the input station for receiving a sheet of paper material or closed during subsequent stations for processing of the sheet. As shown best in FIG. 4, each roller 25 and 26 is mounted for rotation via pin 27 which is held in place by a snap ring 28.

[0027] A plurality of actuators or arms 29 are mounted on axle 20 and spaced at regular intervals to correspond with the location of grippers 9. Each actuator includes a roller 30 at its outer end which extends through an opening 31 formed in upper wall 3 of gripper bar 1 to engage the underside of upper finger 10 and move finger 10 upwardly through its travel to form gap 19 when axle 20 is rotated between its first and second positions. The movement of levers 23 and 24 resulting in the rotation of axle 20 and movement of actuators 29, must be properly coordinated in order to open and close fingers 10 and 11 at the appropriate locations and times and to provide the proper travel or gap 19.

[0028] Referring now specifically to FIG. 3, there is illustrated the hollow hexagonal-shaped profile of gripper bar 1. As illustrated, upper wall 3 and lower wall 4 are parallel to one another, are substantially flat or planar in shape, and have a constant equal thickness of approximately 5 mm. Upper wall 3 has a leading end 32 and a trailing end 33 which define a width for gripper bar 1. Lower wall 4 is spaced from upper wall 3 to define a height for gripper bar 1 which is sufficient to accommodate axle 20 and actuators 29. Lower wall 4 has a leading end 34 and a trailing end 35 which define a width for lower wall 4 which is less than the width of upper wall 3. Leading wall 5 extends between and is integral with the leading ends 32 and 34 of the upper and lower walls 3 and 4 respectively. Leading wall 5 includes a front top wall portion 36 which extends transversely or downwardly from the leading end 32 of upper wall 3 to a front lower end 37 which defines a height for the front top wall portion 36 which is less than the height of bar 1. Leading wall 5 also includes a front bottom wall portion 38 which extends between the front lower end 37 of front top wall portion 36 and the leading end 34 of lower wall 4. As shown best in FIG. 3, the front bottom wall portion 38 is disposed at a first acute angle A1 with respect to the front top wall portion 36. This acute angle A1 preferably ranges from 30° to 80° and is most preferably 74°. The trailing wall 6 extends between and is integral with the trailing ends 33 and 35 of the upper and lower walls 3 and 4 respectively. The trailing wall 6 includes a rear top wall portion 39 extending transversely or downwardly from the trailing end 33 of upper wall 3 to a rear lower end 40 which defines a height for rear top wall portion 39 which is less than the height of bar 1, but equal to the height of front top wall portion 36. Trailing wall 6 also includes a rear bottom wall portion 41 which extends between the rear lower end 40 of the rear top wall portion 39 and the trailing end 35 of lower wall 4. The rear bottom wall portion 41 is disposed at a second acute angle A2 with respect to rear top wall portion 39. As with angle A1, angle A2 is preferably between 30° to 80°, but is most preferably equal to angle A1 and has an angle of 74°.

[0029] Gripper bar 1 is preferably composed of aluminum, and in order to provide sufficient resistance to bending and torsional forces applied during processing of a sheet of paper material, front top wall portion 36 and rear top wall portion 39 both have a thickness greater than the thickness of upper wall 3 and lower wall 4. As illustrated, the front top wall portion 36 and rear top wall portion 39 have a thickness of about 6 mm. However, the ratio of the thickness of wall portions 36 and 39 with respect to upper lower walls 3 and 4 may range from 1.01 to 1 to about 2 to 1, preferably 1.1 to 1 to about 1.5 to 1, and most preferably 1.2 to 1. In addition, it can be seen that front bottom wall portion 38 and rear bottom wall 41 both have tapered thicknesses that gradually decrease from the lower ends 37 and 40 of wall portions 36 and 39 respectively to the leading end 34 and trailing end 35, respectively, of lower wall 4. As illustrated in FIG. 3, the tapered thickness of bottom wall portions 38 and 41 is at an angle of about 5°, but may range between an angle of about 1° to about 10°. These angles are designated as B1 and B2 in FIG. 3. Thus, the increased thickness of top wall portions 36 and 39 with respect to upper and lower walls 3 and 4, together with the tapered thickness of bottom wall portions 38 and 41 serve to minimize stresses applied to gripper bar 1 as gripper bar 1 proceeds in the machine direction between the processing stations. As a result of less stress, gripper bar 1 is less likely to fracture and/or crack.

[0030] Referring now to FIGS. 5 and 6, lever 24 is illustrated in more detail. Lever 24 is identical to lever 23 and thus the following description relating to FIGS. 5 and 6 apply equally to the structure of lever 23. As illustrated, axle 20 has a key or flat area 42 formed in its outer surface at the end thereof. Lever 24 in turn includes a key-receiving opening 43 formed therein which receives the end of axle 20 and includes a matching flat section 44 formed on the inner surface of opening 43 which corresponds in size and dimensions to key 42. In addition to opening 43, lever 24 includes a pair of spaced ears 45 and 46 for mounting roller 26 therebetween (shown in FIG. 1 but not in FIGS. 5 and 6). In order to securely mounting lever 24 on axle 20, lever 24 includes a pair of opposing jaws 47 and 48 surrounding axle 20. Jaws 47 and 48 extend in the opposite direction from ears 45 and 46 and project beyond the circumference of axle 20 to provide a clamp for clamping lever 24 onto axle 20. In order to accomplish this, each jaw 47 and 48 includes a threaded opening 49 and 50 respectively, which receives a retainer or bolt 51 therein. When tightened, bolt 51 securely clamps lever 24 onto axle 20. This clamping action together with the key arrangement formed between axle 20 and lever 24 substantially prevents lever 24 from loosening on axle 20. Thus, this mounting arrangement minimizes the possibility of lever 24 loosening on axle 20. 

I claim:
 1. A gripper bar for gripping a sheet of paper material in a die cutting machine that processes said sheet into a box blank, comprising: a longitudinally extending hollow bar which includes an upper wall having a leading end and a trailing end which define a width for said bar, a lower wall spaced from said upper wall to define a height for said bar, said lower wall having a leading end and a trailing end which define a width for said lower wall which is less than the width of said bar, a leading wall extending between and integral with the leading ends of said upper and lower walls, said leading wall including a front top wall portion extending transversely from the leading end of said upper wall to a front lower end which defines a height for said front top wall portion which is less than the height of said bar, and a front bottom wall portion extending between the front lower end of said front top wall portion and the leading end of said lower wall, said front bottom wall portion disposed at a first acute angle with respect to said front top wall portion, and a trailing wall extending between and integral with the trailing ends of said upper and lower walls, said trailing wall including a rear top wall portion extending transversely from the trailing end of said upper wall to a rear lower end which defines a height for said rear top wall portion which is less than the height of said bar, and a rear bottom wall portion extending between the rear lower end of said rear top wall portion and the trailing end of said lower wall, said rear bottom wall portion disposed at a second acute angle with respect to said rear top wall portion; and a plurality of grippers disposed on said bar and spaced at regular intervals along its longitudinal length.
 2. The gripper bar of claim 1 wherein said upper and lower walls are parallel.
 3. The gripper bar of claim 1 wherein said upper and lower walls are planar.
 4. The gripper bar of claim 1 wherein said upper and lower walls are of equal thickness.
 5. The gripper bar of claim 1 wherein said front and rear top wall portions are parallel.
 6. The gripper bar of claim 1 wherein said front and rear top wall portions are planar.
 7. The gripper bar of claim 1 wherein said front and rear top wall portions are of equal thickness.
 8. The gripper bar of claim 1 wherein the height of said front top wall portion is equal to the height of said rear top wall portion.
 9. The gripper bar of claim 1 wherein said first and second acute angles range from about 30° to about 80°.
 10. The gripper bar of claim 1 wherein said first and second acute angles are equal.
 11. The gripper bar of claim 1 wherein said first and second acute angles are both about 74°.
 12. The gripper bar of claim 1 wherein said upper wall has a thickness, and said front top wall portion has a thickness greater than the thickness of said upper wall.
 13. The gripper bar of claim 1 wherein said upper wall has a thickness, and said rear top wall portion has a thickness greater than the thickness of said upper wall.
 14. The gripper bar of claim 1 wherein said upper wall has a thickness, and said front and rear top wall portions each has a thickness greater than the thickness of said upper wall.
 15. The gripper bar of claim 14 wherein a ratio of the thicknesses of said front and rear top wall portions to the thickness of said upper wall ranges from about 1.01 to 1 to about 2 to
 1. 16. The gripper bar of claim 15 wherein said ratio is from about 1.1 to 1 to about 1.5 to
 1. 17. The gripper bar of claim 15 wherein said ratio is about 1.2 to
 1. 18. The gripper bar of claim 1 wherein said front bottom wall portion has a tapered thickness that gradually decreases from the front lower end of said front top wall portion to the leading end of said lower wall.
 19. The gripper bar of claim 1 wherein said rear bottom wall portion has a tapered thickness that gradually decreases from the rear lower end of said rear top wall portion to the trailing end of said lower wall.
 20. The gripper bar of claim 1 wherein said front bottom wall portion has a tapered thickness that gradually decreases from the front lower end of said front top wall portion to the leading end of said lower wall and said rear bottom wall portion has a tapered thickness that gradually decreases from the rear lower end of said rear top wall portion to the trailing end of said lower wall.
 21. The gripper bar of claim 20 wherein the tapered thickness of said front and rear bottom wall portions is at an angle of from about 1° to about 10°.
 22. The gripper bar of claim 21 wherein the angle is about 5° for both said front and said rear bottom wall portions.
 23. The gripper bar of claim 1 wherein the hollow bar is composed of aluminum.
 24. A gripper bar for gripping a sheet of paper material in a die cutting machine that processes said sheet into a box blank, comprising: a hollow bar defining a longitudinal axis; a plurality of grippers disposed on said bar and spaced at regular intervals along said longitudinal axis and movable between open and closed positions; a longitudinally extending axle rotatably mounted within said hollow bar for movement between a first position wherein said grippers are closed and a second position wherein said grippers are open; a plurality of actuators mounted on said axle and spaced at regular intervals to correspond with said grippers, said actuators rotatable with said axle to open and close said grippers; a lever disposed at one end of said axle operable to rotate said axle between said first and second positions; and mounting means for mounting said lever on said axle, said mounting means comprising a key formed on said axle, a key-receiving opening formed in said lever, and a clamp for clamping said lever on said axle.
 25. The gripper bar of claim 24 wherein said key comprises a flat area formed in said axle and said key-receiving opening includes a matching flat section corresponding thereto.
 26. The gripper bar of claim 24 wherein said clamp comprises a pair of opposing jaws surrounding said axle.
 27. The gripper bar of claim 26 wherein said clamp further includes a retainer for pinching said jaws together about said axle. 